The crash requirements for M1 homologated vehicles (passenger cars) are highly evolved around the shape of existing cars and car design has evolved to meet existing safety legislation.
When a non-conventional car design is proposed it brings problems due to the need to meet current requirements that are designed for conventional vehicle designs.
For example, a standard 40% offset crash requirements when applied to a sub-one meter wide car (such as a 0.8 m wide car) means in the case of a vehicle having two front crash rails:                1) the vehicle will only overlap by 320 mm with the barrier;        2) the main crash rail needs to be within this 320 mm wide zone;        3) space is required outboard of the main crash rail for the wheel and the complete tire envelope when the wheel turns;        4) a wheel envelope for a narrow tire of 0.130 m width and an overall diameter of 0.56 m requires approximately 0.3 m (assuming a 40 degree wheel turn angle);        5) the rail will only overlap the barrier by approximately 0.020 m and a rail of 0.02 m width is not suitable to meet crash requirements;        6) there is only 0.08 m from the edge of the barrier to the centerline of the vehicle; and        7) the maximum width for both crash rails together including any gap in between, is therefore 0.2 m.        
The strategy of using two symmetrical crash rails in parallel will not work for such a narrow vehicle and a single crash device (a crash can unit) located on a centerline of the vehicle is all that can sensibly be packaged.
A second problem is that such a narrow car must still meet forward field of view regulations but the A-pillar structures conventionally used at the front of a vehicle take up a much bigger proportion of the front area in the case of such a narrow vehicle thereby resulting in a disproportionately small front windscreen opening.
The smaller the car, the bigger proportion of the total weight that is allocated to features that cannot be scaled such as the doors. The weight of a door that allows an occupant to exit in comfort, is safe, and includes the same features as the door of a large car is problematic for a small car. A narrow sub-one meter small car is too narrow to seat two occupants side-by-side and although providing a door on both sides is convenient, it is not necessary. The removal of one of the doors will at least partially address the weight allocation problem.